Some new designs of mobile communication devices support multiple Subscriber Identity Module (SIM) cards that provide users with access to multiple separate mobile telephony networks. Examples of mobile telephony networks include GSM, TDSCDMA, CDMA2000, and WCDMA. Example multi-SIM mobile communication devices include mobile phones, laptop computers, smart phones, and other mobile communication devices that are enabled to connect to multiple mobile telephony networks. A mobile communication device that includes two SIM cards that share one radio frequency (RF) resource for communicating with their respective mobile telephony networks and connects to two separate mobile telephony networks is termed a “dual-SIM-dual-standby (DSDS) communication device” or a “DSDS communication device.” A DSDS communication device, like other computing devices that connect to a cellular telephone network, are commonly referred to as “user equipment” or “UE.”
A DSDS communication device may include one shared RF resource that the two subscriptions use to communicate with their respective mobile telephony networks. Only one subscription at a time may use the shared RF resource to communicate with its mobile network. However, even when a subscription is in “standby” mode, meaning it is not currently actively communicating with the network, it may still need to perform discontinuous reception (DRX) operations to receive network paging messages at regular intervals (i.e., a discontinuous reception period) in order to remain connected to the network. Paging intervals for different subscriptions are not necessarily the same nor are they synchronized. Therefore, occasionally the multiple subscriptions sharing an RF resource may need to use the RF resource to communicate with their respective mobile networks simultaneously. To accommodate such network access “collisions,” DSDS communication devices may perform IDLE mode activities for one subscription in IDLE mode even when the other subscription is in a dedicated state, such as conducting a voice call.
Cellular telephone technologies include power management processes coordinated by a communication network base station (nodeB) that function so that the UEs' transmissions are received by the base station with about the same power level, which is a power level high enough to reliably receive the uplink signals, but not so high that UE batteries are drained unnecessarily or so high as to interference with other UEs communicating with the base station (i.e., the “near-far problem”). This requirement is very stringent in technologies that are interference limited, such as CDMA/WCDMA. Typically, the nodeB monitors the signal strength of signals received from each UE and frequently instructs each UE to increase or decrease its transmission power to maintain the received power in a desired band that minimizes interference with other users' uplink power control. In order to control a UE's transmission power, a nodeB compares the measured signal-to-interference ratio (SIR) of a UE's received signals and compares the measured SIR with a target SIR. If the measured SIR is less than the target SIR, the nodeB will request the UE to increase its power by sending a power up command. Otherwise, the nodeB may request the UE to decrease its power by sending a power down command.
This process functions very well for conventional cellphones, enabling the overall communication network, including the nodeB transmitters and the UEs, to optimize network bandwidth and power resources. However, a DSDS communication device with a single transceiver chain may behave in ways that can disrupt the conventional transmission power management process in a manner that can result in misallocation of network resources and unnecessary transmissions of power-up commands. This is because some DSDS communication devices manage network collisions by briefly pausing active subscription's transmissions and tuning the transceiver to another frequency to enable the other subscription to use the transceiver chain for its IDLE mode activities, followed by retuning the transceiver to the frequency of the active subscription. This process of briefly tuning the transceiver chain to support IDLE mode communications is referred to as a “tuneaway” routine. While tuneaway enables the non-active subscription to maintain a link to its network, the result is a brief gap in the transmissions of the active subscription, which is referred to herein as a “tuneaway gap.” During a tuneaway gap in DSDS communication device transmissions, the nodeB will not receive replies to pages and may treat such reception gaps as evidence that the channel has degraded for that particular UE because the nodeB receives no indication when the UE tunes away. In response, the nodeB will send power up commands to the UE and increase its own transmission power on the affected channel as is the normal procedure when a channel degrades. If the channel has not degraded during the tuneaway gap (as will most often be the case), such power up commands are unnecessary. As a result, the UE may experience unnecessary battery drain when its transmission power is unnecessarily increased, and the nodeB may misallocate bandwidth resources to a channel that is not degraded, which can interfere with other UEs communicating with the nodeB. When the tuneaway is over and the UE resumes transmissions on the active subscription, the nodeB will note its signal strength and send power-down commands; however, the power-down process takes a while before the UE returns to the minimal power required for the current link.